A purge system is required on all subatmospheric refrigeration systems, and may be used on non-subatmospheric systems, to remove air, moisture and other noncondensable gases that leak or otherwise enter into the system. The present invention is directed to improvements in such purge systems to reduce the emissions of condensable gases that may accompany the purging or release of the non-condensable gases from the system.
For example, refrigeration systems such as centrifugal chillers, including, for example, the CenTraVac(copyright) centrifugal chillers manufactured by The Trane Company, a Division of American Standard Inc., utilize low pressure refrigerants such as CFC11, CFC113, HCFC123 and multi-pressure refrigerants such as CFC-114 and CFC245A to operate at less than atmospheric pressure, either at all times or under a set of operating or standdown conditions. Since the chillers are operating at subatmospheric pressures, air and moisture may leak into the machine through these low pressure areas. Once the air and moisture and other non-condensables enter the chiller, the noncondensables accumulate in the condenser portion of the chiller during machine operation. The non-condensable gases in the condenser reduces the ability of the condenser to condense refrigerant, which in turn results in an increased condenser pressure, and thereby results in lower chiller efficiency and capacity.
A purge device is a device mounted externally to the chiller. The purge device, in its simplest form, consists of a tank, inlet and outlet connections and valves, and an arrangement for cooling the tank. The arrangement for cooling the tank can be a refrigeration system but may also be a source of cold water or other fluid, a fan system, or even cooled refrigerant from the system being purged. The evaporator or cooling coil of the purge refrigeration system is located within the purge tank and is called the purge evaporator. The purge tank is connected to the chiller system by supply and refrigerant lines through which refrigerant may freely flow. The supply line is typically connected to the condenser and the return line may be connected to the condenser or to the evaporator depending upon the inclusion of a device to maintain system pressures. The purge evaporator includes a coil representing a cold condensing surface to the chiller refrigerant entering the tank through the supply line. When the purge refrigeration unit is running, refrigerant from the chiller condenser is attracted to the cold surface of the purge evaporator in the purge tank. When the gaseous refrigerant contacts the cool surface of the purge evaporator coil, the gaseous refrigerant condenses into a liquid, leaving a partial vacuum behind. More refrigerant vapor from the chiller condenser migrates to the purge tank to fill this vacuum. The liquid refrigerant condensed in the purge tank returns to the chiller system via the return line. Any noncondensables in the vapor from the chiller do not condense in the purge tank and are left behind to fill more and more header space in the purge tank. Increasing quantities of noncondensables accumulating in the purge tank act to reduce the heat transfer efficiency of the evaporator coil, and the leaving temperature will begin to decrease in response thereto. The leaving temperature is monitored by the unit controls, which will activate a pumpout cycle to remove accumulated noncondensables from the purge tank. When enough noncondensables have been removed, the increasing purge compressor suction temperature will terminate the pumpout cycle. Such a system is implemented by Trane and sold under the trademark Purifier(trademark), and is further described in U.S. Pat. No. 5,031,410 to Plzak et al., the disclosures of which are commonly owned and which are incorporated by reference herein.
While the Purifier(trademark) purge has been an industry leader for many years, there are improvements in improving the efficiency of its operation and reducing the percentage of condensable gases escaping with the release of noncondensable gases.
It is an object, feature and advantage of the present invention to solve the problems of the prior art purge systems.
It is an object, feature and advantage of the present invention to provide a purge tank for condensing condensable gases and accumulating noncondensable gases where the purge tank includes baffles.
It is a further object and feature of the present invention that these baffles comprise flat copper discs brazed directly to the top and bottom of an evaporator coil located within the purge tank.
It is an object, feature and advantage of the present invention to increase the rate of removal of noncondensable gases.
It is a further object, feature and advantage of the present invention to modulate the pumpout compressor flow capacity. In one embodiment, this is accomplished by cycling the compressor or its flow components. Cycling flow components includes controlling a pumpout solenoid valve on the suction side of a pumpout compressor during a pumpout cycle.
It is a further object, feature and advantage of the present invention that the solenoid valve be pulsed on and off when the pumpout cycle is initiated so that an adaptive setpoint for the pumpout compressor capacity can be adjusted to full capacity when a feedback sensor indicates that a need for full capacity exists.
It is a still further object, feature and advantage of the present invention that the value of a feedback sensor be measured and compared to a setpoint value to determine whether the pumpout cycle should be initiated, continue or cease.
It is an object, feature and advantage of the present invention to provide adaptive pumpout setpoints that vary during the pumpout cycle.
It is a further object, feature and advantage of the present invention that these adaptive pumpout setpoints be determined as a function of the temperature of condensed liquid refrigerant being returned to the chiller system.
The present invention provides a purging device for a system accumulating condensable and non-condensable gases. The purging device comprises: a purge tank; an inlet connection to the purge tank for receiving the condensable and non-condensable gases from the system and directing said gases into the purge tank; refrigeration means associated with the purge tank for condensing the non-condensable gases into a condensed form; header space in the purge tank for accumulating the non-condensable gases; a first outlet connection for returning the condensed gases from the purge tank to the system; a second outlet for controllably removing the accumulated non-condensable gases from the header space; and a baffle in the purge tank for providing a controlled flow space for the condensable and non-condensable gases and providing a quiet zone in the header spacer.
The present invention also provides a device for separating non-condensable gases from condensable gases. The device comprises: a separation tank having an inlet and an outlet; a heater located in proximity with the separation tank and providing a source for heating the tank; a substance having an affinity for one of the condensable gases and a heat exchanger located within the separation tank in heat exchange relationship with the heater and the substance. The substance is located within the separation tank between the inlet and the outlet so as to capture the gas for which the substances affinity lies. The substance releases the captured gas in response to the application of heat by the heater, and/or reduction of pressure by connection to the low pressure point of the chiller.
The present invention additionally provides a method of determining a setpoint for a purge system. The method comprises the steps of: determining a chiller condensing temperature based upon a temperature of condensed liquid being returned from the purge system to a system being purged; determining a pumpout initiate setpoint as a function of the purge liquid temperature.
The present invention further provides a method of determining a setpoint for a purge system. The method comprises the steps of: determining a chiller condensing temperature based upon a temperature of condensed liquid being returned from the purge system to a system being purged; determining a pumpout terminate setpoint as a function of the purge liquid temperature.
The present invention still further provides a method of determining setpoints for a purge system. The method comprises the steps of: determining a chiller condensing temperature based upon a temperature of condensed liquid being returned from the purge system to a system being purged; determining a pumpout initiate setpoint as a function of a purge operating condition; and determining a pumpout terminate setpoint as a function of the purge operating condition.
The present invention moreover provides a method of controlling the pumpout of a purge tank which contains non-condensable gases extracted from a refrigeration system. The method comprising the steps of: pulsing an outlet control valve for a predetermined amount of time; determining a pumpout initiate setpoint; measuring temperature associated with the purge tank; comparing the measured temperature with the initiate setpoint; initiating continuous pumpout if the suction temperature is less than the initiate setpoint; determining a terminate setpoint; and comparing the suction temperature to the terminate setpoint and terminating pumpout if the measured temperature is greater than the terminate setpoint.
The present invention yet further provides a method of adaptively controlling the operation of refrigeration system. The method comprises the steps of: monitoring the operation of a chiller to determine the time when the chiller is on and the time when the chiller is off; monitoring the operation of a purge system removing non-condensable gases from the chiller to determine when the chiller is pumping out non-condensable gases in terms of when the chiller is on and off; and adaptively modifying the control of the purge in response to the monitored data.